 
mark=int(input("请输入一个数"))
if 90 <= mark <= 100:
        print("A")
elif mark >= 80:
        print("B")
elif mark >= 70:
        print("C")
elif mark >= 60:
        print("D")
elif 0 <= mark < 60:
        print("E")
else:
      print("data error!")
